The present invention relates to compositions suitable for use as lubricant additives which contain an ester-substituted hindered phenol antioxidant and other additives suitable for lubricants such as a detergent or a dispersant. The present invention provides an economical antioxidant which has good performance properties when used in lubricant formulations especially for heavy duty diesel engines and passenger car crankcase.
U.S. Pat. No. 5,523,007, Kristen et al., Jun. 4, 1996, discloses a lubricant oil composition comprising a diesel engine lubricating oil and, as antioxidant, a compound of the formula 
X can be xe2x80x94CH2xe2x80x94CH2xe2x80x94C(xe2x95x90O)xe2x80x94OR and R is a straight chain or branched alkyl radical of the formula xe2x80x94CnH2n+1 wherein n is an integer from 8 to 22.
U.S. Pat. No. 3,285,855, Dexter et al., Nov. 15, 1966, discloses stabilization of organic material with esters containing an alkylhydroxyphenyl group. The ester can have the structure 
in which x has a value of from 0 to 6, inclusively, and y has a value of from 6 to 30, inclusively. The xe2x80x9clower alkylxe2x80x9d groups can be t-butyl. Organic materials which can be stabilized include, among many others, lubricating oil of the aliphatic ester type, and mineral oil.
U.S. Pat. No. 5,206,414, Evans et al., Apr. 27, 1993, discloses a process for the preparation of compounds of the general formula 
A can be xe2x80x94OR4 where R4 can be C2-C45 alkyl.
The present invention provides, among other advantages, a convenient method for obtaining a certain class of hindered phenolic ester antioxidants having particularly useful properties. In particular the antioxidants (shown below), that is, those having an R3 group of 2 to 6 carbon atoms, can be conveniently prepared in a single step. In a preferred synthesis, no trans-esterification reaction is necessary, resulting in a simplified process which leads to fewer byproducts. The antioxidants thus prepared impart excellent thermal and oxidative stability to lubricant formulations and show excellent performance in seal durability tests.
A composition comprising;
(A) at least one antioxidant of the formula 
xe2x80x83wherein R3 is an alkyl group containing 2 to 6 carbon atoms; and
(B) at least one component selected from the group consisting of dispersants and detergents.
Various preferred features and embodiments will be described below by way of non-limiting illustration.
Oil of Lubricating Viscosity
Although not required in all embodiments of this invention, commonly an oil of lubricating viscosity is employed as a medium dissolving or dispersing the other components. Oils of lubricating viscosity include natural and synthetic lubricating oils and mixtures thereof. These lubricants include crankcase lubricating oils for spark-ignited and compression-ignited internal combustion engines, including automobile and truck engines, two-cycle engines, aviation piston engines, and marine and railroad diesel engines. They can also be used in gas engines, stationary power engines, and turbines. Automatic transmission fluids, transaxle lubricants, gear lubricants, metal-working lubricants, hydraulic fluids and other lubricating oil and grease compositions can also benefit from the incorporation therein of the compositions of the present invention.
Natural oils include animal oils and vegetable oils (e.g., castor oil, lard oil) as well as liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic or mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils. Synthetic lubricating oils include hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene-isobutylene copolymers, poly(1-hexenes, poly(1-octenes), poly(1-decenes), and mixtures thereof); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, and di(2-ethylhexyl)-benzenes); polyphenyls (e.g., biphenyls, terphenyls, and alkylated polyphenyls), alkylated diphenyl ethers and alkylated diphenyl sulfides and the derivatives, analogs, and homologs thereof.
Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, or similar reaction constitute another class of known synthetic lubricating oils. These are exemplified by the oils prepared through polymerization of ethylene oxide or propylene oxide, the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methylpolyisopropylene glycol ether having an average molecular weight of 1,000 diphenyl ether of polyethylene glycol having a molecular weight of 500-1,000, diethyl ether of polypropylene glycol having a molecular weight of 1,000-1,500) or mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C3-C8 fatty acid esters, or the C13 Oxo acid diester of tetraethylene glycol.
Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, and alkenyl malonic acids) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, and propylene glycol). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid.
Esters useful as synthetic oils also include those made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, and tripentaerythritol.
Unrefined, refined and rerefined oils (and mixtures of each with each other) of the type disclosed hereinabove can be used in the lubricant compositions of the present invention. Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations, a petroleum oil obtained directly from distillation or ester oil obtained directly from an esterification process and used without further treatment would be an unrefined oil. Refined oils are similar to the unrefined oils except that they have been further treated in one or more purification steps to improve one or more properties. Many such purification techniques are known to those of skill in the art such a solvent extraction, acid or base extraction, filtration, percolation, or similar purification techniques. Rerefined oils are obtained by processes similar to those used to obtain refined oils which have been already used in service. Such rerefined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques directed to removal of spent additives and oil break-down products.
The aliphatic and alicyclic substituents, as well as aryl nuclei, are generally described as xe2x80x9chydrocarbon-basedxe2x80x9d. The meaning of the term xe2x80x9chydrocarbon-basedxe2x80x9d as used herein is apparent from the following detailed discussion of xe2x80x9chydrocarbon-based substituent.xe2x80x9d
As used herein, the terms xe2x80x9chydrocarbon-based substituent,xe2x80x9d xe2x80x9chydrocarbyl substituentxe2x80x9d or xe2x80x9chydrocarbyl group,xe2x80x9d which are used synonymously, are used in their ordinary sense, which is well-known to those skilled in the art. Specifically, any of these terms refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include:
(1) hydrocarbon substituents, that is, aliphatic (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic-, aliphatic-, and alicyclic-substituted aromatic substituents, as well as cyclic substituents wherein the ring is completed through another portion of the molecule (e.g., two substituents together form a ring);
(2) substituted hydrocarbon substituents, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon substituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);
(3) hetero substituents, that is, substituents which, while having a predominantly hydrocarbon character, in the context of this invention, contain other than carbon in a ring or chain otherwise composed of carbon atoms. Heteroatoms include sulfur, oxygen, nitrogen, and encompass substituents as pyridyl, furyl, thienyl and imidazolyl. In general, no more than two, preferably no more than one, non-hydrocarbon substituent will be present for every ten carbon atoms in the hydrocarbyl group; typically, there will be no non-hydrocarbon substituents in the hydrocarbyl group.
Preferably, the hydrocarbon-based substituents in the compositions of this invention are free from acetylenic unsaturation. Ethylenic unsaturation, when present, preferably will be such that no more than one ethylenic lineage will be present for every 10 carbon-to-carbon bonds in the substituent. The hydrocarbon-based substituents are usually hydrocarbon in nature and more usually, substantially saturated hydrocarbon. As used in this specification and the appended claims, the word xe2x80x9clowerxe2x80x9d denotes substituents or groups containing up to seven carbon atoms; for example, lower alkoxy, lower alkyl, lower alkenyl, lower aliphatic aldehyde.
The amount of lubricating oil in a fully formulated lubricant of the present invention (including the diluent or carrier oils present in additive packages) is typically 80 to 99.5 weight percent, preferably 85 to 96 weight percent, and more preferably 90 to 95 weight percent. The lubricating oil can also be used to prepare concentrates containing the additives of the present invention in higher concentrations. The amount of such oil in a concentrate is typically 20 to 80 weight percent.
(A) The Antioxidant
The present invention comprises a hindered, ester-substituted phenol such as one represented by the formula 
and more preferably 
In these structures R3 is a straight chain or branched chain alkyl group containing 2 to 6 carbon atoms, preferably 2 to 4, and more preferably 4 carbon atoms. R3 is most preferably an n-butyl group.
Hindered, ester-substituted phenols of this type can be prepared by heating a 2,6-dialkylphenol with an acrylate ester under base catalysis conditions, such as aqueous KOH.